The production of hydrocarbons from synthesis gas, i.e. carbon monoxide and hydrogen (the Fischer-Tropsch process) is well known. Suitable Fischer-Tropsch catalysts comprise a metal selected from Group VIII of the Mendeleev's Periodic Table of the Elements. Depending on the catalyst composition different products are obtained.
The Fischer-Tropsch process is highly exothermic and temperature-sensitive. High temperature leads to improving the catalyst activity however the selectivity for the main products drops because of by-product formation, such as methane and carbon dioxide. For the creation of the innovative, effective and selective catalysts there is a need in innovative solutions, which provide stability to overheating and hence isothermality of the reactor. Therefore the effective production of hydrocarbons from synthesis gas requires new type catalysts.
One of the methods for overcoming the process problem in a fixed bed reactor is increasing of the heat conductivity of the pelletized catalyst. In this case the heat-conducting materials are used for the Fischer-Tropsch catalysts. It is known that the heat-conducting materials are used as support of the catalysts.
For example, RU2256501 relates to a catalyst for synthesis of hydrocarbons from CO and H2 based on cobalt. The catalyst comprises the powder of metallic aluminium as support that provides high heat conductivity. The catalyst is prepared as follows: the aluminium powder is impregnated with an aqueous solution of cobalt nitrate. Then the impregnated powder is dried on water bath and calcined at 450° C. for 1 hour. However the catalyst has low selectivity and productivity on the main products.
RU2326732 provides the catalyst pellets for synthesis of hydrocarbons from CO and H2 comprising a metal of the VIII group of the Mendeleev's Periodic Table of the Elements and metallic aluminium. The document provides the following preparation method of the catalyst: the active metal (5-40% by weight based on the total weight of the catalyst) is applied by impregnation to the support which is prepared from a paste by extrusion; the paste comprises an oxide component (aluminium oxide and/or silicon oxide and/or titanium oxide and/or zirconium oxide), 1-25% wt metallic aluminium in the form of scales and 5-15% wt boehmite SB-1. The support (that contains the oxide component, the powder of metallic aluminium, diethyl ether, a binder, water, a plasticizer and a pore-forming component) is prepared by extrusion, drying, calcinating, and then the consecutive stages of the impregnation of the support with an aqueous solution of the salt of the active metal are carried out. The support can contain 0.1-5% by weight of a promoter (zirconium or a metal of the VIII group of the Mendeleev's Periodic Table of the Elements and/or oxides) introduced by impregnation with an aqueous solution of the salt of the promoter. However the active component is applied to the support by impregnation, it results in overconsumption of the expensive active metal because the support contains both oxide component and metallic aluminium.
U.S. Pat. No. 6,642,281 discloses using of dispersed active metals, particularly Raney cobalt, as active component in the catalytic hydrogenation of CO. The catalyst is prepared by alloying of cobalt with aluminium, titanium, silicon or zinc, cooling, comminuting of the alloy to a fine powder followed by chemical extraction or dissolution of aluminium, titanium, silicon or zinc. Here Raney cobalt (skeletal cobalt) is used as separate catalyst in catalytic hydrogenation. Such catalyst is stable but quite expensive due to the high content of the cost intensive components. It is impossible to prepare such catalyst in pellets or in block.
U.S. Pat. No. 4,826,799 relates to catalyst pellets for hydrogenation and a preparation method thereof. The catalyst contains 15-50 weight parts of Raney metal, 1-30 weight parts of high polymer (e.g., polyethylene), 1-42 weight parts of α-oxide of aluminium and homogeneous filler. 0-40 weight parts of mineral oil is used as a plasticizer. The mixture is formed by extrusion or alloying, the polymer and the plasticizer are removed by calcination at a temperature of 850-1200° C. Once the alloys are formed, they are treated to extract aluminium with sodium hydroxide.
Therefore the catalysts and the preparation methods have the following principal drawbacks: high cost due to high content of the expensive components; low heat conductivity of pellets; difficulty and need of high temperature processing that requires special equipment, increase the catalyst cost and makes difficult the preparation method.
Summarizing the aforesaid, a need exists for an improved effective and selective, low cost catalyst which is stable to overheating. As well as there is a need in a simple preparation method of the catalyst.